It has long been known to associate sound tapes or sound film with motion picture film in a synchronized manner, so that when projecting the motion picture film or tape, corresponding sound can be generated which is coherent and intelligible, and associated with the pictures being presented by the projection of the motion picture film. It has been known before, for example, to have magnetic tape capable of having audio signals implanted thereon, glued, coated or striped on celluloid or other similar light sensitive photographic film having pictures exposed and developed thereon. Hereafter in this specification, the term "photographic film" shall be used to designate any film which when exposed to light frequencies will be permanently altered so as to record the light frequencies so exposed. Such film is typically celluloid and light sensitive, but may be another construction. The term "picture", moreover, shall be used hereafter to designate the image or collection of light frequencies so exposed to, and recorded on such photographic film.
Such photographic film arrangements, however, have proved extremely difficult and expensive to produce. For instance, the magnetic tape which is compositionally different from the typically celluloid photographic film, must be in some way coated on, or made to adhere to the photographic film. The audio must be recorded on the magnetic strip in a separate operation. Additionally, as the composite, tape and film are being processed through the conventional photographic film processing systems, the magnetic tape must be protected so that it will not be scratched or otherwise altered as to its magnetic composition or structure. While the audio fidelity generated from the magnetic tape is extremely high, it can be appreciated that such a process of developing and recording the photographic film and magnetic tape combination is extremely difficult and expensive.
It has long been known to expose audio signals onto such photographic film. At least as early as the 1930's when the talkies motion pictures were in still early stages of technological development, light was modulated by audio frequencies through a light valve, and exposed to such photographic film. In such arrangements, light was directed into a shutter arrangement within the light valve, consisting of a pair of opaque ribbons oppositely disposed to each other on either side of the light path and surrounded by a strong magnetic field. The ribbons were vibrated into and out of the light path by virtue of audio-frequency current fed to the ribbons. The ribbons therefore increased or decreased the amount of light passing through the light valve. The varied density of the light was then exposed to a track on the photographic film.
Such an audio recording has proven to be inadequate in several respects for high fidelity requirements of audio playback. Frequently, the recorded audio track was scratched, so that the pure dark portions of the audio track might have transparent scratches thereon. Frequently, nontransparent dust and other particles were attached to the transparent portions of the audio track at the crucial moment when light was projected through the audio track for the ultimate audio playback in the projecting theatre. Such factors cause undesired variations of the intended light projection, and consequently noise to the audience. Moreover, with age the celluloid film might scratch, deteriorate, tear or wear away so that the audio sound signals ultimately reproduced by the projection of light through the transparent portions of the audio modulated light exposed track were found to be extremely faulty.
Various experiments in such audio modulated light exposed film audio tracks were performed, and occasionally improvements were realized. See for example Frayne, et al., "An Improved 200-Mil Push-Pull Density Modulator," 47 J. Soc. Mot. Pic. Engr., at page 494.
It has long been known to use push-pull electrical signal modulating arrangements in order to eliminate noise, even-order harmonic distortion, and other spurious signals in an electrical signal where signal purity is an important quality. Thus for example, a signal is split, for example, by a transformer, into two equal signals and transmitted to the point of signal pickup or playback. In the signal pickup, the two signals are superposed on each other in electrical phase difference of 180.degree.. In such out-of-phase superimposition, any extraneous, in-phase noise or other undesirable signal finding its way into the modulated signal of the two signals inherently will be canceled. The perfect, desired signal is thereby reproduced. Noises and other spurious signals which find their way onto the parallel signal paths will be canceled by virtue of the superimposition of the 180.degree. electrical out-of-phase transmission.
It has previously been impossible to record such push-pull signals superimposed, on celluloid or similar type light sensitive photographic film using a cathode-ray tube type of light source in synchronized switched order. This invention and my work are to be distinguished from the work performed independently by Petro Vlahos. The work of Petro Vlahos is described in U.S. Pat. No. 3,969,593 issued July 13, 1976. I expressly disclaim being the inventor of the concept or technique of making substantially noise free sound recordings on color film by modulating discrete, selected color light frequencies by the audio frequencies, with two of the light frequency beams modulated in 180.degree. out-of-phase or push-pull relation, and synchronously superimposing the beams to form a common light frequencies beam for exposing the light sensitive film; and I disclaim being the inventor of means for reproducing audio signals from a plurality of such sound tracks by projecting the audio tracks onto a light dividing prism to divide the light into distinct colors which are received by proper photodetectors; which was described by Petro Vlahos to me.